It is generally accepted that feeding the newborn infant human milk has a positive effect on the infant's health, supplying both optimal nutrition and decreasing the rates of certain infectious diseases. The mechanism by which the latter is achieved is not totally understood, but is thought to be related to the large number of milk components that are classically related to host defense, such as phagocytic cells, immunoglobulins and multiple "nonspecific" factors. Paradoxically, however, milk polymorphonuclear leukocytes (PMN), the most prominent cellular component of colostrum, are hypofunctional compared to the circulating PMN, suggesting that either their intended functions have been performed and they are effete, or that they function in ways that are neither understood nor appreciated. This section of the Program Project Grant proposes to examine three hypotheses about the colostral PMN. The first is that it is an exudate cell, and as such, has the functional behaviour of an exudate cell perhaps with some modifications due to the unique environment in which it exists. The second is that as yet unrecognized components of milk and colostrum uniquely benefit the newborn infant by ameliorating the functional defects found in the neonatal PMN. The third hypothesis is that colostrum and milk are inherently "anti-inflammatory" to protect the neonatal intestine from the potentially harmful effects of maternal PMN that are present in colostrum.